Post-Combustion CO2 capture (PCC) technologies seek to eliminate CO2 from the exhaust of existing stationary fossil fuel burning facilities such as coal or gas fired power stations, cement kilns or furnaces by adding a retrofit plant with minimal disruption to the existing facility.
The total cost of CO2 capture from power station flue gases and compression to pipeline conditions has been estimated to be competitive with other carbon avoidance technologies but significantly above the cost of carbon emissions considered economically acceptable. Thus to be economically acceptable, the difference between the cost of capture and the proposed cost to emit must be met with technical developments that substantially reduce the capital and operating cost of PCC plant.
The conventional PCC process is centred on packed beds with, in the latest developments, customized structured packing and an ‘advanced’ solvent package of blended amines, promoters, anti-corrosion and foam suppressing additives. Packed beds represent a very high interfacial area density (area per unit volume), however, the opportunity for further improvement is limited by the fact that the energy necessary to create surface area by distributing the liquid over the packing surface is provided by gravity alone while the tower diameter is fixed by the maximum allowable gas velocity to limit liquid entrainment or prevent flooding. For a given solvent package and throughput of flue gas (project scale) the size of the column is essentially fixed.
Conventional packed bed designs have limitations in respect to mass transfer performance and the ability of a single design to handle a range of liquid properties (e.g. viscosity).
It is an object of the invention to overcome one or more of the limitations of existing gas absorption/desorption in general and more specifically those used in PCC processes to a significant extent by introducing a different mechanism of contact between the gas and the liquid. The invention enables a liquid sheet to take on duel functionalities of a mass transfer medium and preferably a gas conveyance means. This is achieved through the liquid sheet forming at least part of a gas channel wall, with this liquid sheet possessing rotational motion such that the gas is conveyed along the gas channel or pathway in an analogous fashion to the operation of a metering screw, auger, fan or turbine. The invention advantageously controls the fluid dynamics between the phases without the need of metal packing surfaces and by adding energy more efficiently via the liquid phase which is then transferred to the gas phase.
In a first aspect, the invention provides, a gas and liquid phase contactor comprising                a vessel comprising an inner wall; a pressurised source of liquid; and a gas inlet communicating with a gas and liquid phase contacting space within the vessel,        a distributor apparatus for distributing liquid in the vessel, comprising                    at least one housing rotatable about an axis of the housing;            each rotatable housing having a distributor region comprising at least one liquid outlet or arrangement of liquid outlets arranged in a formation in and around the housing for directing liquid through the gas liquid contacting space towards the inner wall of the vessel,the distributor apparatus having a liquid inlet for introducing liquid into the housing from the pressurised source of liquid and providing pressurised liquid to the at least one liquid outlet or arrangement of liquid outlets, the pressurised liquid in the housing projecting from the housing as at least one liquid sheet rotating around a central axis of the housing towards the inner wall of the vessel; the liquid sheets having two sides and the gas inlet directing gas through the gas liquid contacting space into contact with each side of the at least one liquid sheets projected from the outlets in the housing.                        
The liquid outlets may be a slit shaped orifice or arrangement of slit shaped orifices formed in the distributor region of the housing. The liquid outlets formed in the wall of the housing communicate with the interior of the housing thus providing a passage for liquid through the housing wall. The liquid outlets form an arrangement representing a curve in and around the external surface of the housing extending across the surface of the distributor region of the housing. The liquid outlets may be spaced around the housing in a helical, spiral or other suitable arrangement and shaped to project liquid from the interior of the housing in a liquid sheet. The pitch of the liquid outlets is preferably in the range of 0.2 to 6 times the liquid distributor outer diameter, more preferably 3 to 3.5 times liquid distributor outer diameter.
Within the context of the invention, a helical arrangement or helix includes arrangements where outlets form a curve around the housing with a constant or varying pitch and also spiral arrangements which may not fall within the mathematical definition of a helix but have the appearance of a helix.
The apparatus for distributing liquid is preferably positioned within a vessel and provided with a liquid inlet communicating with a distributor apparatus for distributing liquid within a gas and liquid phase contacting space in the vessel. The liquid distributing apparatus may further be provided with a source of pressurised liquid such as providing liquid via a pump through the liquid outlets in the distributor apparatus to project liquid from the housing at least initially, in a stream of liquid extending continuously along the length of the liquid outlet corresponding to the arrangement, and a gas inlet communicating with the gas liquid contacting space, the gas inlet directing gas into contact with the liquid sheets projected from the outlets in the housing.
In a second aspect there is provided a distributor apparatus for distributing liquid in a vessel, comprising:                at least one housing rotatable about an axis of the housing;        each rotatable housing having a distributor region comprising at least one liquid outlet or arrangement of liquid outlets arranged in a helical or spiral formation in and around the housing for directing liquid through the gas liquid contacting space towards the inner wall of the vessel,        the distributor apparatus having a liquid inlet for introducing liquid into the housing from the pressurised source of liquid and providing pressurised liquid to the at least one liquid outlet or arrangement of liquid outlets, the pressurised liquid in the housing projecting from the housing as at least one liquid sheet rotating around a central axis of the housing towards the inner wall of the vessel; the liquid sheets having two sides and the gas inlet directing gas through the gas liquid contacting space into contact with each side of the at least one liquid sheets projected from the outlets in the housing.        
The design of the vessel (length and diameter) and the housing (length, inside and outside diameter and the shape of the liquid outlet or outlets in the housing) is optimized to suit the design basis of the system and the physical properties of the gas and liquid streams. The gas flowrate, the liquid flowrate, the rotation rate of the housing and the width of the liquid distributor slit are parameters that are preferably adjustable in operation by a processor having a control algorithm to enable the liquid outlets to distribute the liquid as sheets across the majority, if not all of the space between the liquid distributor outlet and the vessel wall thus maximizing the overall performance in terms of mass, momentum and heat transfer as required by the system.
The housing and the inner wall of the vessel are preferably separated by a void. The void functions as a space for which the liquid sheets can be projected, enabling each side of the liquid sheet to interface with a gaseous phase, when the contactor in operation. The void is preferably annular.
The contactor further comprises a pressurised source of liquid, preferably a pump connect to a source of water, for providing liquid through the liquid outlets in the distributor apparatus to project liquid from the housing at least initially, in a stream of liquid extending continuously along the length of the liquid outlet corresponding to the arrangement.
Preferably, the contactor further comprises a rotational drive arrangement to rotate the distributor apparatus about its axis of rotation. The distributor apparatus is preferably rotated at in excess of 1 rpm, more preferably at least 10 rpm and even more preferably at least 100 rpm and yet even more preferably at least 500 rpm. The greater the rotational speed the higher the throughput of the contactor.
The rotational motion exerted upon the liquid sheets has a number of advantages including:                improving mass transfer between the gaseous and liquid phase;        reducing entrainment of the gas in the liquid phase;        stabilising the liquid sheet thereby enabling thinner continuous sheets to be formed; and        imparting a pumping or driving motion to the gas to pump or drive the gas through the gas/liquid contacting space.        
The housing of the liquid distributor may be axially aligned with the gas and liquid phase contacting space although other orientations are possible. This will generally give the housing a vertical orientation.
Preferably the formation of the outlets in the distributor region is helical, spiral or other suitable arrangement and creates a liquid sheet or sheets in a helical pattern or that other suitable arrangement which ideally extends to the radial boundaries of the gas and liquid phase contacting space (i.e. to the inner wall of the vessel). The pitch of the slit or slits is preferably in the range of 0.2 to 6 times the liquid distribution tube outer diameter, more preferably 3 to 3.5 times liquid distribution tube outer diameter. This equates to a pitch angle of approximately 45 degrees.
The distributor apparatus may be formed from a single housing. Alternatively the distributor apparatus may be of modular construction so that the multiple housings are aligned axially. Preferably, each housing has a separate liquid collection region and a pump for each liquid collection region.
In one embodiment, the apparatus further comprises an adjustment device comprising a rod located within an internal passage of the housing and extending along the central axis of the housing; and rod is attached to the housing by an adjustment arm, the adjustment arm being moveable relative to the housing or rod, such that it is able to compress or stretch the housing to thereby reduce or enlarge the width of the liquid outlet. The movement of the adjustment arm relative to the housing or rod may be achieved through a screw mechanism or the like. A key component of the invention is the liquid sheet which functions as a mass transfer and preferably a transport medium to the gaseous phase. In the context of this and other aspects of the invention, a liquid sheet is a stream of liquid which, at least initially, is continuous along the length of the liquid outlet or slit shaped orifice. In order to form a liquid sheet from the liquid outlet, the liquid outlet ideally should be an orifice having a continuous opening along its length. The depth of the orifice and the velocity of the liquid passing through the orifice will also impact upon whether the liquid exiting the orifice is in the form of a liquid sheet. The person skilled in the art is readily able to design the orifice to produce a liquid sheet for a given liquid and flowrate.
Preferably, the liquid outlets or slits have an aspect ratio greater than about 5, so that the length dimension of the slit is about 5 times the width dimension. More preferably, the slits have an aspect ratio of greater than about 10, even more preferably greater than about 20 and yet even more preferably greater than about 50.
Preferably, the length of the liquid outlets or slits extending along the length of the housing is at least 2 times the effective diameter of the housing (i.e. >2 D), more preferably greater than 4 D, even more preferably at least 6 D, yet even more preferably at least 10 D and most preferably at least 20 D. For the purposes of this invention, the effective diameter of the housing is the diameter determined from converting the cross-section area of the housing into a circle. Preferably, the length of the liquid sheet is approximately the length of the liquid outlet from which they are derived.
Preferably, a plane running parallel though the axis of the housing will intersect at least 2, more preferably at least 4, even more preferably at least 8 times and yet even more preferably at least 16 times through the at least one liquid outlet or arrangement of liquid outlets. This configuration of the liquid outlet(s) assists the liquid sheets formed therefrom to function as the walls of a conveying gas channel which contains and transfers the gas phase.
The liquid outlets may also include an arrangement of slit shaped orifices in an arrangement, preferably a helical arrangement. In embodiments in which the slit shaped orifices are in a helical arrangement, the slit preferably extends at least 2 turns (i.e. at least 720 degrees), even more preferably at least 5 turns, yet even more preferably at least 10 turns and most preferably at least 20 turns around the housing. The greater the number of turns, the greater the length of the gas channel that the resulting liquid sheets form, which thereby enables the residence time of the gas in the gas and liquid contacting space to be increased, thus increasing mass transfer between the gas and liquid phase. It will be understood that the number of turns may be spread across one or more modular sections of the gas and liquid contactor (as illustrated in FIG. 2) to avoid the liquid phase becoming saturated with target components from the gaseous phase.
The width of the liquid outlets may be adjusted by an adjustment device. As the material of the housing has an amount of resilience, the adjustment mechanism preferably adjusts the length of the rotating housing, thus adjusting the width of the liquid outlets. By contracting the axial distance between the ends of the housing the width of the outlets reduces and similarly by lengthening the distance between the ends, the width of the outlets increases. In a preferred form, the adjustment mechanism may be a mechanical device. The adjustment mechanism preferably includes a central rod positioned centrally of the rotatable housing, the central rod having ends engaging with the rotatable housing. The width of the liquid outlets is adjusted by adjusting the length of the central rod in the rotatable housing. This may be achieved by varying the distance between the ends of the central rod engaging with the rotatable housing. One of the ends of the rod may be provided with a screw thread which engages with a complementary thread on the central rod. By winding the rod in or out of the screw thread, the width of the outlets can be decreased or increased.
The gas in the gas and liquid phase contacting space is preferably directed between liquid sheets projected from the outlets of the housing causing the gas to flow through the gas and liquid phase contacting space in a path driven by the rotational motion of the liquid leaving the distributor apparatus.
The gas and liquid phase contacting space is preferably defined by the contact surfaces or sides of the liquid sheet or sheets and the external surface of the housing. The external surface of the housing may be at least partially covered by the liquid phase, by nature of its proximity to the liquid sheet from which liquid may emit onto the surface of the external surface of the housing. To this extent, the external surface of the housing also comprises this incidental coating of liquid.
The liquid sheets preferably extend from the liquid outlets from the housing to the internal wall of the vessel. Once the liquid sheets contact the internal wall of the vessel, it travels along the internal wall towards the liquid outlet of the vessel.
In contrast to conventional gas and liquid phase contactors, the configuration defined under the present invention provides a large interfacial surface area through which both free surfaces of the liquid sheet(s) form part of the gas and liquid phase contacting space. As the gas and liquid contact in the space or void between the rotatable housing and the inner wall of the vessel, the space preferably has an annular configuration. To minimise the proportion of the gas and liquid phase contacting space in which none or only one side of the liquid sheet forms part of the gas and liquid phase contacting space, the distance that the liquid sheet travels from the liquid outlet to the inner wall of the vessel is increased and/or the distance between each liquid sheet (e.g. vertical distance when housing is vertically mounted) is reduced. This arrangement minimises the proportion of the gas and liquid phase contacting space which is defined by the external surface of the housing (no liquid sheet interface) or the internal wall of the vessel (interface with one side of the liquid sheet). The rotating liquid sheets form gas channels defined by the contacting surfaces of the liquid sheets, the external surface of the housing and the internal surface of the vessel. The rotating motion of the liquid sheets drives or pumps the gas through the space between the housing and the internal surface of the vessel in an auger or screw thread action. When the outlets are arranged in a helical or spiral arrangement around the housing, the liquid sheets form a helical or spiral arrangement around the housing in an annular space.
Accordingly, from a cross-sectional view through the vessel, the number of contacting spaces on either side of the housing within the vessel is preferably at least 4 (FIG. 1 illustrates 4 contacting spaces), more preferably at least 10, even more preferably at least 30 and yet even more preferably at least 50.
After passing through the gas and liquid phase contacting space, the gas may then be exhausted from the gas and liquid phase contacting vessel through a gas outlet.
The liquid may be collected in at least one liquid collection region and removed through a liquid outlet.
In the context of a gas liquid contacting apparatus, the liquid absorbs or desorbs a component of the gas in the gas and liquid phase contacting space and so the liquid in the liquid collection region is higher/lower in that component of the gas than liquid entering the vessel. This liquid may subsequently be passed to a desorption/absorption process to reclaim/strip the component or at least a portion of the stream may be recycled to re-enter the distributor apparatus.
In contrast to existing packed bed columns, the gas and liquid phase contactor of the present invention has the ability to be optimised for different gas/liquid systems. For example, the contactable surface area may be adjusted through the liquid mass flow rate; the dimensions of the liquid distributor, which themselves can be adjusted by a suitable mechanism such as that associated with the central rod; and the rotation rate of the liquid distributor. This ability to dynamically adjust the gas and liquid phase contactor enables mass transfer rates to be continuously optimised for a gas and liquid phase system as well as enabling the one gas and liquid phase contactor to be used for different applications each requiring different parameter settings.
Preferably, the apparatus of the first aspect or the gas and liquid phase contactor of the second aspect of the present invention further comprise a control unit. The control unit preferably comprises a computer aided control system or is configured to control the liquid distributer or the gas and liquid phase contactor algorithms to control and optimise mass, heat and/or momentum transfer between the gaseous and liquid phases. The computerised control system preferably comprises computer software comprising algorithms that control and optimise mass, heat and/or momentum transfer between the gaseous and liquid phases. The algorithm or algorithms preferably use chemical and process parameters of the gas liquid system, such as the liquid's viscosity and available mass transfer data. Preferably, the algorithm or algorithms can use performance data of the apparatus or gas and liquid phase contactor to provide correlated equations to further optimise the process.
Preferably, the algorithm or algorithms set operating parameters to maximize the mass transfer performance of the device while minimizing the energy requirements of the process. Liquid and gas flowrates are preferably set by the algorithm to meet the specific process and performance requirements while the algorithm or algorithms are able to further adjust the rotation rate and the gap spacing such that the fluid dynamic performance is maintained over a required range of performance. The width of the liquid opening may be controlled by means of a mechanical adjustment of the length of the housing. The stability of the liquid sheet is determined by the viscosity and surface tension of the liquid, the velocity and thickness of the sheet which diminishes as the liquid extends out from the liquid distributor. Preferably the algorithm or algorithms maximize the overall performance by adjusting the operating parameters to maximize both the mass transfer and the gaseous output or pumping capacity.
In a third aspect, the first or second aspect is used in the absorption and/or desorption of gases in PCC.
In a fourth aspect, there is provided a process for desorption and/or absorption of a gas phase with a liquid phase comprising the steps of:                (A) providing a pressurised source of liquid to a housing comprising at least one liquid outlet or arrangement of liquid outlets arranged in a formation in and around the housing;        (B) forming the pressurised liquid phase in the housing into at least one liquid sheet by projecting the pressurised liquid in the housing from the housing through the at least one liquid outlet or arrangement of liquid outlets in the housing; each liquid sheet comprising two sides; and        (C) contacting the gas phase with each side of the two sides of the at least one liquid sheet,        wherein the at least one liquid sheet forms at least part of a gas channel wall defining a gas and liquid phase contacting space through which the gas phase flows and wherein the at least one liquid sheet is in rotational motion around a central axis of the housing.        
Preferably the liquid sheet makes up at least 50%, more preferably at least 70% and even more preferably at least 90% of the total surface area of the gas channel wall.
The liquid phase may be a slurry (solid/liquid phase) or an emulsion (mixed liquid phase). In embodiments when the liquid phase is a slurry, the width of the liquid outlet is preferably less than 25%, and more preferably less than 15% of the mean maximum diameter of the particles in the slurry mixture. This assists in preventing the solid particles blocking the liquid outlet.
Preferably, the gas is transported through the vessel by the action of the at least one liquid sheets in rotational motion around a central axis.
Preferably, a control unit, as previously described, is used to implement the process according to this aspect and may be used to form the at least one liquid sheet from the liquid phase.
In one embodiment the gas and liquid phase contacting space is a single helical gas channel. In alternative embodiments, the liquid contacting space comprises multiple gas channels, either helical or the resulting multiple pathways which exists around the liquid sheets projected from the liquid outlets.
The rotational motion of the liquid phase is preferably generated by a rotational drive arrangement to rotate the distributor apparatus about its axis of rotation which may be provided in the first and/or second aspect of the present invention. Preferably the gas is transported through the gas channel substantially by means of the rotational motion of the liquid sheet (i.e. no or minimal external pumping means for the gas is required.).
The geometry of the contacting space or gas channel (e.g. length, turns and pitch etc) may be designed to suit a particular application.
In a fifth aspect, there is provided a control unit characterised by means which are designed to carry out the process of the fourth aspect of the present invention.
As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps.
For the purposes of the present invention, the use of the singular form shall also encompass that of the plural form, unless otherwise indicated.
For the purposes of the present invention, the term liquid sheet is a two sided liquid sheet (i.e. both free surfaces are in contact with a gaseous phase), unless otherwise indicated. Reference to the liquid coated inner wall of the vessel is reference to a single sided liquid sheet.
For the purposes of the present invention, the term “projected” means to send out into space.